205 research outputs found
Bose-Fermi Kondo model with Ising anisotropy: cluster-Monte Carlo approach
The Bose-Fermi Kondo model captures the physics of the destruction of Kondo
screening, which is of extensive current interest to the understanding of
quantum critical heavy fermion metals. There are presently limited theoretical
methods to study the finite temperature properties of the Bose-Fermi Kondo
model. Here we provide some of the consistency checks on the cluster-Monte
Carlo method, which we have recently applied to the Ising-anisotropic
Bose-Fermi Kondo model. We show that the method correctly captures the scaling
properties of the Kondo phase, as well as those on approach to the
Kondo-destroying quantum critical point. We establish that comparable results
are obtained when the Kondo couplings are placed at or away from a Toulouse
point.Comment: 2 pages, 2 figures, to appear in the proceedings of SCES 07 (the
international conference on strongly correlated electron systems 2007
Low-Energy Spin Dynamics of CuO Chains in YBa(2)Cu(3)O(6+x)
We study the spin fluctuation dynamics of Cu-O chains in the oxygen deficient
planes of YBa(2)Cu(3)O(6+x). The chains are described by a model including
antiferromagnetic interactions between the spins and Kondo-like scattering of
the oxygen holes by the copper spins. There are incommensurate spin
fluctuations along the direction of the chains. The dynamic structure factor of
this system is qualitatively different from that of a quasi one-dimensional
localized antiferromagnet due to the presence of itinerant holes. We compute
the dynamic structure factor that could be measured in neutron scattering
experiments.Comment: 2 pages, 2 eps figures, LT22 proceedings, phbauth style file include
A large-N analysis of the local quantum critical point and the spin-liquid phase
We study analytically the Kondo lattice model with an additional
nearest-neighbor antiferromagnetic interaction in the framework of large-N
theory. We find that there is a local quantum critical point between two
phases, a normal Fermi-liquid and a spin-liquid in which the spins are
decoupled from the conduction electrons. The local spin susceptibility displays
a power-law divergence throughout the spin liquid phase. We check the
reliability of the large-N results by solving by quantum Monte Carlo simulation
the N=2 spin-liquid problem with no conduction electrons and find qualitative
agreement. We show that the spin-liquid phase is unstable at low temperatures,
suggestive of a first-order transition to an ordered phase.Comment: 4 pages and 1 figur
Magnetoconductance through a vibrating molecule in the Kondo regime
The effect of a magnetic field on the equilibrium spectral and transport
properties of a single-molecule junction is studied using the numerical
renormalization group method. The molecule is described by the
Anderson-Holstein model in which a single vibrational mode is coupled to the
electron density. The effect of an applied magnetic field on the conductance in
the Kondo regime is qualitatively different in the weak and strong
electron-phonon coupling regimes. In the former case, the Kondo resonance is
split and the conductance is strongly suppressed by a magnetic field , with the Kondo temperature. In the strong
electron-phonon coupling regime a charge analog of the Kondo effect develops.
In this case the Kondo resonance is not split by the field and the conductance
in the Kondo regime is enhanced in a broad range of values of .Comment: 6 pages, 4 figure
Locally critical point in an anisotropic Kondo lattice
We report the first numerical identification of a locally quantum critical
point, at which the criticality of the local Kondo physics is embedded in that
associated with a magnetic ordering. We are able to numerically access the
quantum critical behavior by focusing on a Kondo-lattice model with Ising
anisotropy. We also establish that the critical exponent for the q-dependent
dynamical spin susceptibility is fractional and compares well with the
experimental value for heavy fermions.Comment: 4 pages, 3 figures; published versio
Continuous quantum phase transition in a Kondo lattice model
We study the magnetic quantum phase transition in an anisotropic Kondo
lattice model. The dynamical competition between the RKKY and Kondo
interactions is treated using an extended dynamic mean field theory (EDMFT)
appropriate for both the antiferromagnetic and paramagnetic phases. A quantum
Monte Carlo approach is used, which is able to reach very low temperatures, of
the order of 1% of the bare Kondo scale. We find that the finite-temperature
magnetic transition, which occurs for sufficiently large RKKY interactions, is
first order. The extrapolated zero-temperature magnetic transition, on the
other hand, is continuous and locally critical.Comment: 4 pages, 4 figures; updated, to appear in PR
Quantum Kicked Dynamics and Classical Diffusion
We consider the quantum counterpart of the kicked harmonic oscillator showing
that it undergoes the effect of delocalization in momentum when the classical
diffusional threshold is obeyed.
For this case the ratio between the oscillator frequency and the frequency of
the kick is a rational number, strictly in analogy with the classical case that
does not obey the Kolmogorov-Arnold-Moser theorem as the unperturbed motion is
degenerate.
A tight-binding formulation is derived showing that there is not
delocalization in momentum for irrational ratio of the above frequencies. In
this way, it is straightforwardly seen that the behavior of the quantum kicked
rotator is strictly similar to the one of the quantum kicked harmonic
oscillator, although the former, in the classical limit, obeys the
Kolmogorov-Arnold-Moser theorem.Comment: 9 pages, LaTeX. Comments are welcom
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